Is it "Grey" or "Gray"

[Nami Nami]

when I am referring to the colour between black and white?
when I am referring to the colour of the hair when people get old?
when I am referring to the area of unclear or arguable, e.g.
This is not clearly stated in the contract. It's in grey [or gray] area?

[Alan]

Both spellings are possible!
grey: British English
gray: AmEng